I. Field
The present invention relates to data communication. More particularly, the present invention relates to novel and improved techniques for determining the available transmit power for data transmissions in a wireless communication system.
II. Background
A modern day communication system is required to support a variety of applications. One such communication system is a code division multiple access (CDMA) system that supports voice and data communication between users over a terrestrial link. The use of CDMA techniques in a multiple access communication system is disclosed in U.S. Pat. No. 4,901,307, entitled xe2x80x9cSPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS,xe2x80x9d and U.S. Pat. No. 5,103,459, entitled xe2x80x9cSYSTEM AND METHOD FOR GENERATING WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM.xe2x80x9d A specific CDMA system is disclosed in U.S. patent application Ser. No. 08/963,386, entitled xe2x80x9cMETHOD AND APPARATUS FOR HIGH RATE PACKET DATA TRANSMISSION,xe2x80x9d filed Nov. 3, 1997 (the HDR system), now U.S. Pat. No. 6,574,211, issued on Jun. 3, 2003 to Padovani et al. These patents and patent applications are assigned to the assignee of the present invention and incorporated herein by reference.
CDMA systems are typically designed to conform to one or more standards. Such standards include the xe2x80x9cTIA/EIA/IS-95-B Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular Systemxe2x80x9d (the IS-95 standard), the xe2x80x9cTIA/EIA/IS-98 Recommended Minimum Standard for Dual-Mode Wideband Spread Spectrum Cellular Mobile Stationxe2x80x9d (the IS-98 standard), the standard offered by a consortium named xe2x80x9c3rd Generation Partnership Projectxe2x80x9d (3GPP) and embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the W-CDMA standard), and the xe2x80x9cTR-45.5 Physical Layer Standard for cdma2000 Spread Spectrum Systemsxe2x80x9d (the cdma2000 standard). New CDMA standards are continually proposed and adopted for use. These CDMA standards are incorporated herein by reference.
Some CDMA systems are capable of supporting different types of service (e.g., voice, data, and so on) over the forward and reverse links. Each type of service is typically characterized by a particular set of requirements.
Voice service typically requires a fixed and common grade of service (GOS) for all users as well as a (relatively) stringent and fixed delay. For example, the overall one-way delay of speech frames may be specified to be less than 100 msec. These requirements may be satisfied by providing a fixed (and guaranteed) data rate for each user (e.g., via a dedicated channel assigned to the user for the duration of a communication session) and ensuring a maximum (tolerable) error rate for speech frames independent of the link resources. To maintain the required error rate at a particular data rate, a higher allocation of resources is required for a user having a degraded link.
In contrast, data service may be able to tolerate different GOS for different users and may further be able to tolerate variable amounts of delays. The GOS of a data service is typically defined as the total delay incurred in the transfer of a data message. The transmission delay can be a parameter used to optimize the efficiency of a data communication system.
To support both types of service, a CDMA system can be designed and operated to first allocate transmit power to (voice) users requiring a particular GOS and shorter delays. Any remaining transmit power can then be allocated to (data) users that can tolerate longer delays.
Numerous challenges are encountered in implementing a CDMA system capable of supporting different types of service. First, the transmit power required by voice users can vary during their communication sessions. Consequently, the amount of transmit power available for data users can vary from one (e.g., 20 msec) transmission interval to the next, and possibly even within the transmission interval. Second, the transmit power required for a particular data user may also vary during a data transmission.
The available transmit power for data service and the required transmit power for a particular data transmission are each typically estimated or predicted at a particular moment in time (e.g., at the time data transmissions are scheduled) for a particular future moment in time (e.g., the start of the next transmission interval). However, the link conditions may change during the next transmission interval, and the estimated available and required transmit power may not be accurate over the entire transmission interval. If the estimated available transmit power is too high and/or the estimated required transmit power is too low, excessive frame errors may occur for a data transmission (thereby degrading performance). Alternatively, if the estimated available transmit power is too low and/or the estimated required transmit power is too high, valuable system resources may be under-utilized.
As can be seen, techniques that can be used to accurately estimate the transmit power available for data service and the transmit power required for a data transmission in a CDMA communication system are highly desirable.
The present invention provides techniques to accurately estimate the transmit power available for data transmissions and the transmit power required for a particular data transmission for a future time period (e.g., the next frame). In accordance with one aspect of the invention, variation in the available transmit power over time is estimated. A first margin is then computed and used to account for the estimated variation in the available transmit power. The available transmit power at a future time instance (e.g., the beginning of the next frame) is predicted and reduced by the first margin to derive a more accurate estimate of the available transmit power.
In accordance with another aspect of the invention, variation in the transmit power required for a data transmission to a particular data user is estimated and used in scheduling the data transmission to this data user. A second margin can be computed and used to account for the estimated variation in the required transmit power for this data user. Whereas the first margin accounts for variation in the (overall) available transmit power, the second margin is specific to the link conditions experienced by the data user.
A specific embodiment of the invention provides a method for estimating transmit power available for data transmissions for a future time period (e.g., the next frame). In accordance with the method, a (previously) predicted available transmit power for a prior time instance and a (previously computed) average available transmit power for a prior time period are received. Variation in the available transmit power over time is estimated based on the received predicted and average available transmit power. A margin is then determined to account for the estimated variation in the available transmit power. The available transmit power at a future time instance (e.g., the beginning of the next frame) is then predicted and subtracted by the margin to derive an estimated available transmit power for the future time period.
Other embodiments include methods, schedulers, and other elements that implement various aspects and features of the invention, as described in further detail below.